The present invention relates generally to electroslag refining, and, more specifically, to electroslag refining of superalloys.
Electroslag refining is a process used to melt and refine a wide range of alloys for removing various impurities therefrom. U.S. Pat. No. 5,160,532-Benz et al. discloses a basic electroslag refining apparatus for refining typical superalloys of nickel, cobalt, zirconium, titanium, or iron.
The initial, unrefined alloys are typically provided in the form of an ingot which has various defects or impurities which may be removed during the refining process to enhance metallurgical properties thereof, including grain size and microstructure for example.
In electroslag refining, the ingot is suspended inside a crucible and electrically powered. Slag is electrically heated inside the crucible by current passing between the electrode ingot and the crucible for melting the lower end of the ingot.
As the ingot melts a refining action takes place, with oxide inclusions in the ingot melt being exposed to the liquid slag and dissolved therein. Droplets of the ingot melt fall through the slag by gravity and are collected in a liquid melt pool at the bottom of the crucible, with the slag floating thereatop.
The refined melt is typically extracted from the crucible by an induction-heated, segmented, water-cooled copper guide tube. The guide tube is relatively complex for inductively heating the refined melt as it is drained by gravity therethrough for preventing solidification of the melt which would decrease its discharge or draining rate.
The stream of refined melt discharged from the crucible makes an ideal liquid metal source for many solidification processes including powder atomization, spray deposition, investment casting, melt-spinning, strip casting, and slab casting. In spray forming, the melt is atomized with a suitable atomizing gas and collected on a suitable workpiece or ingot. An atomizer ring is typically mounted directly below the guide tube for receiving the refined melt for atomization thereof.
Spray forming is typically effected at a substantially constant rate of melt delivery, and accordingly the guide tube must be precisely configured and operated to control the induction heating of the discharged melt, as well as the cooling of the guide tube.
At the completion of refining of an individual ingot, the refining process is terminated which causes plugging of the discharge orifice in the guide tube with solidified melt. The orifice is unplugged by physically removing or extracting the plug therefrom which causes wear of the soft copper drain orifice. Accumulation of wear in the orifice over one or more cycles of electroslag refining increases the size of the orifice and can adversely affect the desired flowrate of the refined melt therethrough.
Accordingly, the entire segmented guide tube must be disassembled from the crucible and replaced with new components including a properly sized drain orifice. This correspondingly increases the associated cost of electroslag refining and subsequent spray forming.
It is, therefore, desired to provide an electroslag refining apparatus having an improved discharge guide.
A melt guide includes a base plate having internal cooling channels and a center aperture extending vertically therethrough. A unitary drain bushing is removably mounted in the aperture and is readily replaceable after wear thereof.